The modification of cellulose fibers features has been studied in recent years, since said features directly impact the manufacturing and the final paper characteristics. Among cellulose fibers features, the flexibility and the carboxylic groups number thereof are of great importance to the development of paper having improved mechanic and structural strength.
Enzymatic treatments have been used in processes for manufacturing cellulose fibers, although in most cases they are used aiming only to reduce chemical reagents consumption and to improve the aspects of the effluent generated during the cellulose fiber producing process.
On the other hand, some prior art documents disclose the differences between cellulose fibers and paper features through the application of enzymes only in the manufacturing process of paper.
Document WO03/021033 discloses an enzymatic treatment of cellulose fibers to increase the number of aldehyde groups. These groups become binding sites to hydroxyl groups of the fibers, when they are transformed into a dry sheet of paper, thus increasing the mechanical strength thereof. One of the processes disclosed in said document consists in treating the fibers with one or more hydrolytic enzymes, optionally, in the presence of surfactants, other non-cellulose enzymes or non-hydrolytic chemical reagents wherein the aldehyde groups are formed in or close to the fibers surface. The description shows that the enzymatic treatment is carried out in the approximating circuits of the paper making machine, in such a way that it is also disclosed a process for handling the aqueous suspension containing the aldehyde groups-rich fraction, carrying out the refining and/or additional mixture of further chemical additives, which are common in the paper manufacturing. After the formation of a sheet of paper, white water containing hydrolytic enzymes is collected and recycled in order to increase treatment efficacy.
Document WO00/68500 discloses a process for the production of paper with higher wet strength by treating the fibers with a phenol oxidative enzyme prior to the paper machine circuit, more specifically, in the depuration system. After the enzymatic treatment, the fibers are refined and then mixed with additives which are generally used/required for paper manufacturing.
Document WO2007/039867 discloses differentially densified fibrous structures, processes for making the same, and processes for treating fibers used in the fibrous structures. Fibers treatment was carried out using only cellulases enzymes and no acid step was associated with it. Besides, the purpose was to change paper sheet fibrous structure.
Document PI9505211-9 discloses an acid treatment focused on the hexenuronic acid removal and not in the distinction among the features of fibers. Therefore, the association of the acid step with xylanases enzymes developed according to said state of art document aimed to increase the removal of hexenuronic acids.
Document JP2001303469 discloses processes for bleaching cellulose using an acid-treating step and treatments with xylanases for reducing the amount of used bleaching chemicals required during fibers bleaching step and also to allow obtaining and separating xylooligosaccharide compounds from the generated filtrate.
Document JP2004060117 discloses a process for bleaching pulp, wherein an enzymatic treatment is used after pulp bleaching step using chlorine dioxide.
Document WO9844189 discloses processes for treating cellulose fibers in order to remove color (chromophores groups) by the application of cellulase, with pH 3.0 to 7.0, and xylanase, with pH 5.5 to 9.0. The aim of applying cellulase is to open the cell wall pores in the fibers to increase the ability of xylanase to remove the chromophores. Another treatment for preparing the fibers (increasing the swelling, and therefore enlarging the pores) is carried out using low molecular weight amine (e.g. methylamine). The enzymatic treatment is not found in association with an acid step and it also does not present any results of flexibility modification and carboxylic groups of the fibers, related to the alteration of the strength and drainage/drying.
Document U.S. Pat. No. 7,144,716 discloses a process for immobilizing enzymes through the application thereof in a pH ranging from 5.0 to 6.9. The obtained results describe only the maintenance or decrease in the enzyme activity either as a function of immobilization or not, when subjected to different shear stresses (stirring).
Document PI0517695 discloses a process for modifying fibers aiming to increase the wet strength of the paper sheet. The modification is carried out through the use of cellulose derivatives (e.g. CMC=carboxymethyl cellulose) not using enzymes. Although it uses the association of the CMC-based treatment with an acid step, it is not related to the use of enzymes.
Mora et al (1986) describes the enzymatic action for treatments performed with retention times of 24 and 88 hours in medium containing HgCl2 (extremely harmful to the environment and to human health) in order to inhibit the action of cellulases, enabling the evaluation of the individual effect of the xylanases. The used temperature equals to 40° C. and the pH was not specified. The association of the enzymatic treatment with an acid step aiming to distinct the fibers was never mentioned.
Noe et al (1986) describes the enzymatic action for treatments performed with retention times of 2 to 54 hours, in a medium containing HgCl2, in a temperature of 40° C. It comprises a acid washing step to denature the enzyme in order not to promote changed in the fibers. This document teaches that although the enzymatic treatment leads to improvements in the refine process, and consequently in fibers properties (e.g. flexibility), it shows that in non-refined pulps the enzymatic action itself is not sufficient to provoke changes in the cell wall of fibers, which are required for increasing of the swelling thereof, and consequently, for increasing fibers flexibility. Nevertheless, this document does not contain any description or even a suggestion on which additional treatments could be associated with the enzymatic treatment so as to obtain the desired fiber properties.
Bajpai et al (2006) describes the action of combinations of Laccase-mediator enzymes, Laccase-mediator with xylanases and Laccase-mediator with xylanase and an acid step aiming to improve the ECF bleaching, but it does not describe the effect on pulp quality, nor the possibility of using these combinations for the distinction among fibers properties. In view of that, there is a need for developing processes which result in a significant distinction in cellulose fibers features. Among said processes, those using an enzymatic treatment show a high potential in fulfilling this need.
Therefore, it is the object of the present invention to fulfill said need existing in the state of art of obtaining cellulose fibers.